Intercalating purple membranes into 2D β-alanine crystals to enhance photoelectric and nonlinear optical properties

Abstract

β-Alanine crystals with addition of purple membranes (PM) containing photoactive bacteriorhodopsin were prepared and characterized. Adding PM slightly to the crystals caused neither significant changes in their shapes nor shifts in the FTIR, SAXS intensity, and XRD spectra of the mother crystal. However, the purple composite crystal had a lower initial decomposition temperature but also a higher final decomposition temperature than the colorless pure one. The AFM analysis revealed that the embedded PM patches had undergone dynamic transitions, and were intercalated between β-alanine crystal layers with native integrated planar conformations. Compared with the pure one, the composite crystal exhibited 10-fold stronger second harmonic intensities, which varied with the incident angle and polarization of the probe beam. Thousands-fold increases in anisotropic positive photoconductance were also observed with the composite crystal. The results suggest orientational arrangement of most PM patches within each crystal and demonstrate the feasibility of producing a novel composite crystal with improved photonic properties by adding PM.